Chapter 3 – AT Commands,
S-Registers
Certain modem values, or parameters, are stored in memory locations called
Register Unit Range Default Description
Register | Unit |
| Range | Default | Description |
S0 | 1 ring |
| 0, | 1 | Sets the number of rings until the modem answers. ATS0=0 |
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| disables autoanswer completely. |
S1 | 1 ring |
| 0 | Counts the rings that have occurred. | |
S2 | decimal |
| 43(+) | Sets ASCII code for the escape code character. | |
S3 | decimal |
| 13 (^M) | Sets ASCII code for the RETURN character. | |
S4 | decimal |
| 10 (^J) | Sets ASCII code for the LINE FEED character. | |
S5 | decimal |
| 8 (^H) | Sets ASCII code for the BACKSPACE character. | |
S6 | 1 sec. |
| 2 | Sets the time the modem will wait for a dial tone before aborting a | |
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| call. |
S7 | 1 sec. |
| 45 | Sets the time the modem. | |
S8 | 1 sec. |
| 2 | Sets the length of a pause caused by a comma character in a | |
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| dialing command. |
S9 | 100 ms |
| 6 | Sets delay between when the modem detects a valid carrier | |
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| signal and when it turns on its CD circuit. |
S10 | 100 ms |
| 7 | Sets how long a carrier signal must be lost before the modem | |
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| disconnects. S10=255 causes the modem to not disconnect with |
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| loss of carrier. |
S11 | 1 ms |
| 70 | Sets spacing and duration of dialing tones. Recommended | |
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| minimum is 50 ms. |
S13 | decimal |
| 0, | 37 (%) | Sets ASCII code for remote configuration escape character. |
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| S13=0 disables remote configuration. |
S17 | 10 ms |
| 25 | Sets the length of the break time (space) sent to the local PC | |
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| when the modem receives a remote break. |
S24 | 50 ms |
| 20 | Sets the time the DSR, CTS, and CD signals drop before going | |
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| high again. Used for some PBX and CBX phone systems. |
S25 | 100 ms |
| 0, | 0 | Sets the time the DTR signal must be dropped before the modem |
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| disconnects. The 0 default equals 50 ms. |
S30 | 1 min. |
| 0, | 0 | Sets how long the modem waits after the last character is |
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| received or transmitted before it disconnects. The 0 default |
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| disables the timer. |
S32 | 100 ms |
| 20 | Sets the time the modem will wait for a RETURN to be entered | |
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| during escape sequence execution. |
S34 | 1 char |
| 10 | Sets the number of command characters allowed after +++AT. | |
S36 | 1 sec. |
| 0, | 5 | Sets the time between DTR inactive and modem offhook. S36=0 |
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| disables DTR |
S37 | 1 sec. |
| 5 | Sets the time between DTR active and modem | |
S43 | decimal |
| 28, 26, | 0 | Sets fixed V.34 connect speed. 28 = 28800 bps; 26 = 26400 bps; |
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| 24, 21, |
| 48 = 4800 bps. 0 default disables this feature. |
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| 19, 16, |
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| 14, 12, |
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| 96, or 48 |
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S48 | decimal |
| 33, 31, | 0 | Sets maximum V.34 connect speed. 33 = 33600 bps; 31 = 31200 |
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| 28, 26, |
| bps;…48 = 4800 bps. 0 default disables feature (same as |
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| 24, 21, |
| S48=33). |
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| 19, 16, |
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| 14, 12, |
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| 96, or 48 |
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18 |